Device for measuring the intra-ocular pressure

ABSTRACT

A device for measuring intraocular pressure includes a remote measuring device that can be implanted in the eye and that contains a pressure sensor, a device that can convert the sensor signals into information that can be transmitted without wires, and a transmitter. The device also includes a receiving device located outside the eye which receives the information transmitted by the transmitter and which is connected to an evaluation device in which the received information is converted into data on the intraocular pressure for recording.

The invention relates to a device according to the preamble of claim 1.A device of this kind is in known from U.S. Pat. No. 5,005,577.

Measurements of intraocular pressure (glaucoma) are normally conductedon a routine basis during a visit to an eye specialist. In patients withknown glaucoma, pressure measurements are performed at regular intervalsof 6 to 12 weeks. These pressure measurements however are not veryinformative since the intraocular pressure varies with time of day. Toobtain objective information as to whether a pathological pressuresituation exists, continuous pressure measurements must be performedover a long period of time and a decision can be made on their basis asto whether therapy should be initiated, and what kind. This is notpossible with the devices currently available for measuring intraocularpressure (tonometers).

The available tonometers (applanation and impression tonometers) permitan exact determination of the intraocular pressure (Grehn, F.,Leydhecker, W. “Augenheilkunde” [Ophthalmology], 26th edition, SpringerVerlag, pp. 244-5). Their practical reliability for routine earlydetection is limited, however. With the known measuring devices, thecornea of the eye which is sensitive to pain is touched duringmeasurement so that pressure measurement can be performed only followinglocal anesthesia of the eye. The known measuring devices provide valuesthat can not be used, when the surface of the cornea is abnormal as aresult of edema or scars or in astigmatism. Investigations followingoperations on the eye to monitor the success of the operation are notpossible. Non-contact clinometers currently on the market do not achievethe measurement accuracy required for a reliable diagnosis. Especiallyin the high pressure range which results in irreversible damage to theoptic nerves, measurements with the currently available non-contacttonometers are too inaccurate and unreliable. Since the applanation ofthe cornea is used for measurement in these clinometers as well, theysuffer from the disadvantages associated with this applanation.

The device described at the outset known from U.S. Pat. No. 5,005,577includes a remote measurement device that can be implanted in an eyeusing an intraocular lens, said device containing a pressure sensor, adevice that converts the sensor signals into information that can betransmitted without wires, and a transmitter. By means of a receiverlocated outside the eye, the information transmitted by the transmitterthat can be implanted is received and converted into data on theintraocular pressure that can be recorded. In addition, the known devicecan have an energy source supplied from outside, for example aphotoelectric element, to produce an active sensor and telemetrictransmitter for data transmission.

In order to perform objective evaluation as to whether a pathologicoptical situation exists in the eye, pressure measurements must beevaluated that cover a long period of time. Acquisition of theselong-term pressure measurements is cumbersome with the known devices.

Hence the goal of the invention is to provide a device for measuringintraocular pressure with which an elevated intraocular pressure(glaucoma) can be monitored continuously and called up as necessary.

This goal is achieved according to the invention by the characterizingfeature of claim 1.

Using the data logger in the implanted remote measurement device,continuous recording and storage of the measured values are performedover a long period of time. These data can be called up as necessarywithin a short space of time, for example within seconds to minutes. Itis only during this period of time that an auxiliary device, in the formof a manual device, spectacles, or an eye bandage must be used toreceive the measured data.

The remote measuring device which is preferably designed for activetelemetry can be located at a suitable point, for example the sulcus ofthe capsule or the anterior chamber, as an implant that can be installedby surgery. This implant can be in the form of an intraocular lens, withthe remote measuring device being provided outside the optical part ofthe lens, preferably at a haptic margin surrounding the lens part. Thiscreates an intelligent lens for multifunctional measured valueacquisition by active telemetry and integration of the data logger bywhich measured values can be stored.

Suitable sensors are those that allow determination of the intraocularpressure. In particular, the pressure sensor or pressure sensors, incontrast to the known capacitive measuring sensors (Sensors andActuators A, 37-38 (1993) 93-105) can be created using surfacemicromechanics. In addition, electrodes for stimulation and derivationof stimulus potentials can be provided. The pressure sensor, thecorresponding signal processing circuit, the data logger, and thetelemetry components in the sensor, especially the coil and capacitors,are preferably integrated monolithically in a chip, for example asilicon chip. By inductive signal and energy transmission between theimplanted remote measuring device and the receiving device providedoutside the eye, active telemetry is obtained with the power supplied tothe remote measuring device in the eye by inductive energy transmission.For this purpose, both the implanted remote measuring device and thereceiving device located outside the eye have suitably designed antennasin the form of coils (ring coils).

Continuous measurement of intraocular pressure over several stages ispossible without continuous data callup to the outside being necessary.With the data logger integrated into the active telemetry, data can bestored and called up at specific times, once a week for example. Theimplanted sensors can be calibrated without an external device, usingself calibration. No spectacles need be worn for calibration. The energysupplied is reduced in active telemetry. Interference with themeasurement is reduced by the monolithically integrated design. Themeasuring device is EMV tolerant. With a preferred surfacemicromechanical solution, the likelihood of the sensors breaking isreduced. In addition, surface-micromechanical sensors can be made inthat sizes required for implantation. With the monolithically integrateddesign, silicon chips can be made thin enough to fit in the eye implant,especially an intraocular lens. The power can be supplied by inductiveenergy transmission from outside so that no battery is required.

One embodiment of the invention will now be explained in great detailwith reference to the figures.

FIG. 1 is a schematic side view of an embodiment of the invention;

FIG. 2 shows an implant designed as a lens which contains the remotemeasuring device used in the invention; and

FIG. 3 is a block circuit diagram of the implanted remote measuringdevice.

In the embodiment shown in the figures, a remote measuring device 6 isplaced in the eye as an eye implant designed as an intraocular lens 8.Remote measuring device 6 which contains pressure sensors 10 and sensortelemetry components, especially telemetry electronics 11, is located inthe vicinity of a haptic margin 14 surrounding an optical part 9 of theintraocular lens. Pressure sensors 10 can be designed using surfacemicromechanics. Telemetry electronics 11 contain a data logger 16 tostore the measured values received from pressure sensors 10. Inaddition, the telemetry electronics is connected with a coil 15 thatoperates as a transmitting and receiving antenna. The measured datastored in data logger 16 can be called up and sent if necessary byactivating an electronic switch in a transmission circuit 18 connectedwith coil 15. Telemetry electronics 11 as well as pressure sensors canbe integrated monolithically into a silicon chip made so that it fits inthe haptic margin 14 of the lens. Preferably the lens is made of siliconmaterial. Haptic margin 14 has a width of approximately 1 mm. The lensdiameter can vary between 6.5 and 7 mm. The intraocular lens can besecured for example in the capsule of the eye using haptic threads 13.Pressure sensors 10 (sensor components) and the telemetry electronics(read station) with the transponder electronics and the micro-antennadesigned as a coil 15 are in the haptic margin 14 outside the opticalzone 9 of the intraocular lens. The thickness of the lens body dependingon the refractive power can be 1 to 2 mm.

A polydiorganosiloxane, preferably, is used as the implant materialbecause of its good biocompatibility and deformability. The implant canthus be implanted in the folded or even rolled state through a smallincision. A polydiorganosiloxane, especially polydimethylsiloxane, canbe used for encapsulation of the microcomponents of the remote measuringdevice.

The measurement signals generated by pressure sensors 10 as a functionof the measured intraocular pressure are converted by the telemetry andtransponder electronics into information that can be transmitted withoutwires in a converter 17 and transmitted by means of the micro-antennadesigned as coil 15 and received outside the eye by a receiving device 1through an antenna likewise designed as a coil 2. Receiving device 1 andcoil 2 can be located in a spectacle frame 3. However, other securingmeans are also suitable, for example a comfortable eye bandage.Receiving device 1 is connected by a cable 4 with an evaluating device 5in a base unit. This base unit can have a battery for power supply inaddition to the evaluation and interface electronics. However it is alsopossible to provide the energy through a power cable. Evaluation unit 5converts the received information into data that can be recorded. Forthis purpose, a fixed data evaluation device can be provided foroff-line data processing, storage, analysis, and display on a PC.

The power for the remote measuring device 6 implanted in the eye can beprovided by induction through the two coils 2 and 15 that act asantennas during transceiver operation.

What is claimed is:
 1. A device for measuring intraocular pressurecomprising: a remote measuring device adapted to be implanted in an eye,said remote measuring device having a pressure sensor, a converter forconverting sensor signals into information for wireless transmission,and a transmitter; a receiver adapted to be located outside the eye forreceiving information transmitted by the transmitter; and an evaluationdevice for converting information received into data expressing theintraocular pressure and for recording the data, wherein the remotemeasuring device further includes a data logger in which measurementdata continuously supplied by said pressure sensor is stored and fromwhich the measurement data is called up at certain times in operation ofthe converter.
 2. The device according to claim 1 wherein the remotemeasuring device is located in or on an implant.
 3. The device accordingto claim 2 wherein the implant is an intraocular lens.
 4. The deviceaccording to claim 3 wherein the remote measuring device is locatedoutside an optical lens part of the lens.
 5. The device according toclaim 2 wherein the implant is made of a polydiorganosiloxane.
 6. Thedevice according to claim 5, wherein said polydiorganosiloxane ispolymethylsiloxane.
 7. The device according to claim 1 wherein thepressure sensor is designed using surface micromechanics.
 8. The deviceaccording to claim 1 wherein a polydiorganosiloxane is used forencapsulation of microcomponents forming said remote measuring device.9. The device according to claim 8, wherein said polydiorganosiloxane ispolymethylsiloxane.
 10. The device according to claim 1 wherein thepressure sensor, the data logger, and associated signal processing andtelemetry components are fully monolithically integrated.
 11. The deviceaccording to claim 10, wherein said telemetry components include a coiland capacitors.